Many conventional solders contain lead as a major constituent thereof. Such solders often have desirable physical properties, and the use of lead- containing solders is widespread throughout several industries, including those concerned with the production of printed circuit boards.
There are, however, increasing demands for lead-free solders due, for example, to environmental considerations, and it seems likely that, within the next few years, it will be a legal requirement in several countries for solders used in the manufacture of many items to contain little or no lead.
One type of alloy that has been used as a replacement for the conventional tin-lead solders are tin-copper alloys, and an alloy consisting of 99.3% tin and 0.7% copper has become relatively widely used in certain industries. However, the properties of such a tin-copper alloy are less desirable than those of the conventional tin-lead alloy, and in particular the tin-copper alloy exhibits a lower strength, a lower fatigue resistance and a higher eutectic temperature than the conventional tin-lead alloy.
This is particularly undesirable, since many industrial machines and processes are configured to work effectively with the conventional tin-lead alloy, and ideally a lead-free solders replacement should be capable of being used with the same machines and processes without significant modification thereof. Many manufacturers have, however, found that existing soldering processes must now be significantly adapted to accommodate the use of lead- free solders, and this adaptation of processes and materials is widely regarded as a poor use of resources, particularly as the standard of articles manufactured using known lead-free solders is often considerably below that achievable using conventional leaded solders.